1. Field of the Invention
The present invention relates generally to an optical transmission system and, more particularly, is directed to an optical repeater system having an automatic optical by-pass.
2. Description of the Prior Art
Optical transmission lines have recently been replacing conventional electric lines in transmitting information signals from one point to another with a minimum amount of interference. However, as with conventional electric lines, considerable loss of light energy results when such optical transmission lines are used over a relatively long distance. In other words, such optical transmission results in attentuation of the transmitted optical information signals. Accordingly, regenerative repeaters are inserted at different points along the optical transmission lines to amplify the optical information signals so as to compensate for such attenuation. Examples of such systems are shown in U.S. Pat. Nos. 3,801,819; 3,851,167; and 3,943,358.
Unfortunately, if a regenerative repeater fails to operate due to, for example, a defect in the circuitry thereof, or if no operating power is supplied to the regenerative repeater, the optical information signals are not transmitted along the transmission lines.
One system, as shown in U.S. Pat. No. 4,148,558, has been proposed which utilizes two separate optical paths which are alternately positioned in the transmission path by means of a solenoid. The first path includes a glass rod which merely transmits an input optical information signal from an optical input to an optical output. The second path includes a detector for converting the input optical information signal to an electrical signal and a light emitter which functions to convert an electrical signal supplied thereto to an optical signal and to transmit this latter optical signal to the optical output. The electrical signal from the detector is supplied to a utilization device which performs some operation in response to such signal and which supplies an electrical signal to the light emitter which does not correspond to the input optical information signal. Alternatively, the electrical signal produced by the detector can be supplied directly to the light emitter which merely reproduces the input optical information signal without modification. This device, however, does not function as a regenerative repeater to amplify the input optical information signal. In other words, the second path is positioned in the transmission path only during processing of the input optical information signal by the utilization device. Further, if at such time, the power supplied to the system should fail, or if the detector, the light emitter or utilization device should malfunction or fail to operate, no optical signal is transmitted to the optical output. In other words, the first transmission path constituted by the glass rod is not automatically substituted for the second transmission path.